View Full Version : 744 cruise altitude .......
could some one tell me what would be considered the normal max cruise altitude for the 747-400 ........ I'm told its 35,000 which seems a bit on the low side? ....... cheers .....
edit ... upon mature reflection, maybe this is not a question one should ask in an open forum, which I guess, is a sad reflection on the world we live in ...... having said that, I'm going to lose the bet I made ....... oh well .......
Big Kahuna Burger
1st Nov 2002, 23:18
45,100 is the certified max ceiling.
Anyone got a weight/Alt chart to copy and paste?
Notso Fantastic
3rd Nov 2002, 20:13
39,000 is normal maximum operating alt. It can go higher, the cabin differential pressure won't increase- it's already on the maximum at about 8 1/2 psi I think it is, so the cabin altitude will just increase. You have to be fairly light to be able to cruise to make it worth the climb, very light to be able to make it worthwhile going above 39,000'. Everybody is happy that 39,000' is high enough. Delivery flights with no payload would be a good time to try it, or flights with very light /no load.
notso fantastic ..... thanks for that ...... I've won my bet !!!! ..... cheers guys .......
Intruder
4th Nov 2002, 02:22
NotSoFast...
Define "normal max operating alt? before you try to collect.
As BKB said, the max operating alt is 45,100'. However, it is seldom operated at 45,000'.
It is very common to operate at FL370 and FL390. I have cruised at FL410 occasionally, and a few times at FL430. However, the airplane has to be almost empty to operate efficiently at 430.
The normal pressurization differential is about 8.9 psi, and max is 9.2 psi.
Because the amount of time operated at FL410 is relatively small, FL390 might be called the "normal maximum operating alt" by someone, but it is not a commonly defined term...
hi intruder ...... the bet was that 747-400's never exceeded 35,000 ....... this seemed low to me although I accept that load ,weather, traffic and journey distance could all have an impact ...... my view was that something between 39/40,000 would often be achieved ...... we were talking specifically about north atlantic crossings between europe and the U.S.A. (say eight hours typical flight time) .......
I promise you that if I win the bet it wont change my life style ....lol ......
cheers .....
http://www.takeoutaxi.com/images/f-86.gif
Notso Fantastic
4th Nov 2002, 20:32
Intruder- with the loads we carry, operating above 39,000' is virtually unheard of! To do so is more of a pilot 'experiment' exercise ( as in 'been there, done that, got the teeshirt, won't bother again'). It is the 737 that doesn't go above about 35,000'.
cb9002
6th Nov 2002, 21:13
Could someone explain why aircraft become less efficient at these high altitudes? I was of the impression that higher flights are faster, use less fuel and are more comfortable.
Also, I was on a Swiss A330 a month ago, and the inflight display showed a cruise at FL410 - I just thought that was a mistake. Can the buses get that high too?
Intruder
6th Nov 2002, 21:43
>>Could someone explain why aircraft become less efficient at these high altitudes? I was of the impression that higher flights are faster, use less fuel and are more comfortable.
First, the maximum ceiling for an airplane at high gross weights may be less than, or just above 410. If the fuel savings at the higher cruise altitude cannot make up for the fuel burned in the climb, it will actually use more fuel.
Also, depending on the height of the jet stream and tropopause, the most efficient combination of temperature and wind may be at a lower altitude. The colder the air, the lower TAS at a specific Mach number. The TAS (and ground speed, when wind is significant) has to be balanced with fuel burn.
Finally, there is a much smaller airspeed range between stall buffet and Mach buffet at higher altitudes. A bit of turbulence could bounce the airplane into one regime or the other, making both comfort and safety margins suffer.